Intensity modulated radiation therapy (IMRT) is a treatment method for cancer patients requiring radiation treatment. IMRT is an extremely precise method of treatment delivery where the radiation dose conforms to the target and avoids the surrounding critical structures. Rather than having a single large radiation beam pass through the body, with IMRT the treatment is delivered from various angles and the intensity of the radiation beam is varied across the treatment area.
The radiation is effectively broken up into thousands of tiny pencil-thin radiation beams. With millimeter accuracy, these beams enter the body from many angles and intersect on the cancer. This results in a high radiation dosage to the tumor and a lower radiation dose to the surrounding healthy tissues.
One method for modulating the intensity of the radiation beam is based upon moving a multi-leaf collimator (MLC) in and out of radiation beam from the radiation treatment machine. An MLC comprises a plurality of thin width mechanical blades or leaves, which are individually controlled by miniature motors and mechanical drive linkages. A computer controls the miniature motors for driving the individual blades in and out to shape the radiation beam. An advantage of an MLC based IMRT treatment machine is that the same MLC can be automatically controlled to support the individual needs of each patient receiving radiation treatment. In other words, the MLC is reconfigured for each new patient.
Linear accelerators have for decades come with a photon flattening filter to make the photon profile of planar fluence and thus, the dose distribution more uniform. These filters have then resulted in fluence attenuation and contamination of the beam. Now in the age of techniques such as intensity modulated radiation therapy (IMRT) the function of the flattening filter becomes redundant and the flattening filter now merely reduce the efficiency of the beam by reducing the fluence and increase scattered radiation.
Other objects and advantages of the present invention will become apparent to those skilled in the art upon a review of the following detailed description of the preferred embodiments and the accompanying drawings.